This application is based upon and claims the benefit of priority of Japanese Patent Applications No. 2001-232739 filed on Jul. 31, 2001, No. 2001-232746 filed on Jul. 31, 2001, No. 2002-73105 filed on Mar. 15, 2002 and No. 2002-128085 filed on Apr. 30, 2002, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an impeller for feeding fuel under pressure from the interior of a fuel tank to fuel injection system in a vehicle, as well as a turbine type fuel pump which includes the impeller.
2. Description of Related Art
In a vehicle such as an automobile there sometimes is used a turbine type fuel pump for feeding fuel under pressure from the interior of a fuel tank to a fuel injection system. The turbine type fuel pump (also called xe2x80x9cWesco pumpxe2x80x9d) usually includes an impeller of a disc shape having on its outer periphery surface a plurality of blades and blade grooves, a pump housing which houses the impeller therein rotatably, the pump housing having a C-shaped pump channel communicating with the blade grooves, and a motor for driving the impeller.
The fuel pump is required to exhibit a high pump efficiency. For satisfying this requirement it is necessary that {circle around (1)} fuel should flow smoothly from the pump channel into the blade grooves of the impeller and flow out smoothly from the blade grooves to the pump channel, {circle around (2)} there should occur neither stagnation nor collision between fuel flowing out from one-side blade grooves and fuel flowing out from opposite-side blade grooves, {circle around (3)} a larger amount of fuel should rotate within the blade grooves and side grooves, {circle around (4)} pulsation of fuel should not occur at terminal end portions of the side grooves, and {circle around (5)} characteristics (shape and size) of the blade grooves should be capable of being determined while coming to attach importance to the increase of the pressure of fuel.
For the purpose of improving the pump efficiency, a fuel pump disclosed in JP-A No. Hei6-272685 (first conventional example) includes an impeller wherein front wall surfaces of blade grooves in a rotational direction are inclined. As shown in FIGS. 25 and 26, blades 304 and blade grooves 306 are formed alternately in a circumferential direction on both sides of a partition wall 302 of an impeller 300, and a C-shaped pump channel 312 which includes a pair of side grooves 311 is formed in a pump housing 310. The impeller 300 is adapted to rotate in x direction within the pump housing 310.
Front wall surfaces 307 of the blade grooves 306 are inclined to a side (rear side) opposite to the rotational direction x with respect to a plane P which is perpendicular to a side face 301 of the impeller 300, whereby it is intended to cause vortex flows to flow smoothly near the front wall surfaces 307, eliminate the occurrence of a negative pressure thereabouts and thereby prevent the occurrence of a turbulent flow.
In a fuel pump disclosed in JP-A No. Hei 6-272685 (second conventional example), as shown in FIG. 27, blades 321 and blade grooves 322 are formed alternately on both sides of a partition wall 323 of an impeller 320. An outside diameter of an outer periphery surface 323a of the partition wall 323 is equal to an outside diameter of an outer periphery surface 321a of each blade 321. A pump housing 325 has a C-shaped pump channel, the pump channel comprising right and left side grooves 326 and a communicating groove 327 for communication between both side grooves.
As indicated with arrows, fuel enters the inner periphery side of blade grooves 322 from the side grooves 326, then flows radially outwards through the blade grooves 322 while being guided by both side faces 323b of the partition wall 323 under the action of a centrifugal force based on rotation of the impeller 320, whereby the fuel pressure is increased. The fuel thus increased its pressure then flows out to the communicating groove 327 and side grooves 326 from the outer periphery side of the blade grooves 322 and again enters blade grooves 322 located on the back side.
In a fuel pump shown in FIG. 28 (third conventional example), an outside diameter of an outer periphery surface 343a of a partition wall 343 in an impeller 340 is smaller than that of an outer periphery surface 341a of each blade 341, and the width of the partition wall 343 is very small at the outer periphery surface 343a. As a result, right and left blade grooves 342 are communicated with each other through an annular space 344 formed on the outer periphery side of the partition wall 343. A pump channel of a pump housing 345 comprises right and left side grooves 346 and a communicating path 347 which provides communication between both side grooves 346.
Fuel which has entered the inner periphery side of blade grooves 342 from the side grooves 346 flows radially outwards through the blade grooves while being guided by both side faces 343b of the partition wall 343 under the action of a centrifugal force based on rotation of the impeller 340, whereby its pressure is increased. The fuel thus increased its pressure flows out to the annular space 344 and the communicating path 347 from the outer periphery side of the blade grooves 342 and again enters blade grooves 342 located on the back side.
In a fuel pump shown in FIG. 29 (fourth conventional example), the width of a guide surface 363b of a partition wall 363 in an impeller 360 i.e., the width of a bottom of each blade groove 362, increases gradually at an outermost periphery portion, and an annular portion 368 is formed on an outer periphery side of the partition wall 363 and blades 361. On the other hand, in a pump housing 365 is formed a C-shaped pump channel which includes right and left side grooves 366 and a communicating path 367 for communication between both side grooves 366.
In impeller and housing disclosed in Japanese Patent No. 2962828 (fifth conventional example), a communicating portion is not formed in the pump housing, but a communicating hole is formed in the impeller. More particularly, as shown in FIGS. 30 and 31, in one side face 401 on a discharge side of an impeller 400 and in an opposite side face 406 on a suction side of the impeller there are formed plural blade grooves 402 and 407 spacedly in a circumferential direction. Between adjacent blade grooves 402 and 407 are formed blades 403 and 408, and an annular portion 411 is formed along an outer periphery edge of the impeller 400.
The blade grooves 402 in one side face 401 and the blade grooves 407 in the opposite side face 406 have arc shaped bottoms 404 and 409 respectively. The groove bottoms 404 and 409 intersect each other at an axially intermediate portion, whereby a communicating hole 413 extending axially through the impeller from one side face 401 to the opposite side face 406 is formed radially outwards of the intersecting portion indicated at 405. The blade grooves 402 and 407 are in communication with each other through the communicating hole 413.
In FIG. 30, a housing 415 comprises a discharge-side housing 416, a suction-side housing 421, and an outer housing 426. One side groove 417 is formed in an inner surface of the discharge-side housing 416 at a position close to the outer periphery side. The one side groove 417 extends in C shape from a start end portion up to a terminal end portion (neither shown) which is communicated with a fuel discharge port.
Likewise, an opposite side groove 422 is formed in an inner surface of the suction-side housing 421 at a position close to the outer periphery side. The opposite side groove 422 extends from a start end portion communicated with a fuel suction port up to a terminal end portion (neither shown). The outer housing 426 covers outer periphery surfaces of both discharge-side housing 416 and suction-side housing 421.
Fuel flows into the blade groove 407 from a start end portion of the suction-side housing 421, then passes through the communicating hole 413 in the impeller and flows to a start end portion of the opposite-side blade groove 402 and a start end portion of the discharge-side housing 416. While the impeller 400 is rotating, its blades 403 and 408 imparts a circumferential push-out force to the fuel which has entered the blade grooves 402 and 407 and the resulting centrifugal force causes the fuel to flow radially outwards along the groove bottoms 404 and 409.
Thereafter, the fuel strikes against the annular portion 411 of the impeller 400 and flows axially outwards, then is guided by the side grooves 417 and 422 and returns to the blade grooves 402 and 407. While repeating the circulation between the blade grooves 402, 407 and the side grooves 417, 422, the fuel flows spirally from the start to the terminal end portion through the pump channel. The pressure-increased fuel which has reached the terminal end portion of the suction-side housing 421 flows through the communicating hole 413 into the terminal end portion of the discharge-side housing 416 and is discharged from the fuel discharge port.
The construction of the blade groove 306 in the first conventional example shown in FIGS. 25 and 26 cannot be said satisfactory for the improvement of pump efficiency. In more particular terms, radially in FIG. 25, as indicated with arrow y, fuel flows into the blade groove 306 from the inner periphery side thereof, then flows radially outwards while being guided by a side face 303 of the partition wall 302, and flows out from the outer periphery side of the blade groove 306. In the circumferential direction, as indicated with arrow z in FIG. 26, fuel flows into the blade groove 306 from the front wall surface 307 side and flows out from a rear wall surface 308 side.
Since the front wall surface 307 of the blade groove 306, i.e., the rear wall surface of the blade 304, is inclined backward with respect to the rotational direction x, the admission of fuel into the blade groove 306 becomes smooth to some extent. However, since the rear wall surface 308 of the blade groove 306, i.e., the front wall surface of the blade 304, is parallel to the plane P, the efflux of fuel from the blade groove 306 cannot be said satisfactorily smooth. Moreover, there occurs stagnation between fuel portions flowing out into the pump channel from both sides of the partition wall 302, so that the flow rate of circulating fuel is apt to decrease. Further, as shown in FIG. 26, the axial length of the blade groove 306 is short and so it is difficult to consider that a large amount of fuel circulates.
In the second conventional example shown in FIG. 27, fuel present in the blade groove 322 flows radially outwards while being guided by the guide surface 323b of the partition wall 323b, then strikes against an end portion of the communicating groove 327 and its flowing direction is changed to a transversely outward direction. Thus, the fuel present in an intermediate portion of the communicating groove 327, i.e., the fuel present outside the outer periphery edge 323a of the partition wall 323, is apt to stagnate. Consequently, the amount of fuel circulating between the blade groove 322 and the pump channels 326, 326 is apt to decrease.
In the third conventional example shown in FIG. 28, the fuel present in the blade groove 342 flows radially outwards while being guided by the guide surface 343b of the partition wall 343 and strikes against an intermediate portion of the communicating path 347, then its flowing direction is changed substantially to both transversely outward directions. Consequently, the flow velocity of fuel is apt to decrease.
As to the above inconveniences involved in the first to third conventional examples, one cause is presumed to reside in that the impellers 300, 320 and 340 are not provided with an annular portion along the outer peripheries of the partition walls 302, 323 and 343.
According to the fourth conventional example shown in FIG. 29, the width of the partition wall 363 increases gradually toward the outermost periphery, but not to a sufficient extent. Besides, no special consideration is given for preventing the pulsation of fuel and for increasing the flow rate of rotating fuel.
The blade grooves 322 of the impeller 320, the blade grooves 341 of the impeller 340, and the blade grooves 362 of the impeller 360 in the second, third, and fourth conventional examples, respectively, are short in their axial lengths and it is difficult to consider that a large amount of fuel circulates.
In the fifth conventional example shown in FIGS. 30 and 31, it is desirable that characteristics (shape and size) of the blade grooves 402 and 407 be determined while coming to attach importance to an optimum pressure increase of fuel. Therefore, in selecting characteristics of the blade grooves 402 and 407, it is necessary that characteristics of the communicating hole 413 be taken into account. For example, although increasing the blade grooves 402 and 407 is effective in point of increasing the fuel pressure, the communicating hole 413 becomes smaller and a smooth flowing of fuel between the discharge-side housing 416 and the suction-side housing 421 is obstructed. That is, the presence of the communicating hole 413 restricts a free design of characteristics of the blade grooves 402 and 407.
An object of the present invention is to provide an impeller and a turbine type fuel pump superior in pump efficiency by forming an annular portion on an outer periphery side of the impeller to let one- and opposite-side blade grooves independent and by subsequently improving the impeller and/or pump housing.
More specifically, a first aspect of the invention aims at providing a turbine type fuel pump wherein fuel flows smoothly into blade grooves from a pump channel and flows out smoothly from the blade grooves to the pump channel, and the flow of fuel is accelerated within the blade grooves, thereby permitting the flow of fuel in the pump channel to be prevented from stagnation.
A second aspect of the invention aims at providing a turbine type fuel pump capable to prevent stagnation and collision of fuel flowing out from both-side blade grooves, allowing large amount of fuel circulate from the interiors of blade grooves and side grooves, and preventing pulsation of fuel at a terminal end portion of a pump channel.
A third aspect of the invention aims at providing an impeller and a fuel pump both capable to determine characteristics of blade grooves which can realize a higher pump efficiency independently of characteristics of communicating means and capable to prevent movement of the impeller within a pump housing which is caused by imbalance of pressure.
A fourth aspect of the invention aims at providing an impeller and a fuel pump capable to determine characteristics of blade grooves which can realize a higher pump efficiency independently of characteristics of communicating means and permitting an increase in the amount of fuel circulating within the blade grooves.
In connection with the first aspect of the invention, the present inventors have become aware that the impairment of smooth fuel admission into the blade grooves is caused by separation of fuel flow from the inner surface side of the rear wall surface of each blade, that the flow velocity of fuel in each blade groove is influenced by the width (circumferential length) of the blade groove on each of side face and a transversely central side of the impeller, that a vigorous efflux of fuel from each blade groove depends on the shape of an outer periphery side of the front wall surface, and that the stagnation of fuel flow can be prevented by increasing the width of the impeller at the outermost periphery. The present inventors have also taken notice of easiness in molding of the impeller. If the shapes of blade and blade groove are determined taking only pump efficiency into account, a certain shape of blade groove may render the removal of a die after molding impossible.
To achieve the first aspect of the invention, a turbine type fuel pump is provided with an impeller of a disc shape. The impeller has blades, blade grooves, and an annular portion formed on an outer periphery side of the blade grooves. The blades and the blade grooves are formed alternately in a circumferential direction on one side and an opposite side of an outer periphery portion of the impeller. Front and rear wall surfaces of each of the blade grooves are inclined backward with respect to a rotational direction. The fuel pump further has a pump housing which houses the impeller therein rotatably. The pump housing has generally C-shaped side grooves on one and the opposite side which side grooves are in communication with the blade grooves on one and the opposite side respectively, a fuel suction port communicating with a start end portion of the side groove on one side, and a fuel discharge port communicating with a terminal end portion of the side groove on the opposite side.
With the fuel pump mentioned above, by rotation of the impeller, fuel is circulated independently between the side grooves on one and the opposite side and the blade grooves on one and the opposite side to increase the fuel pressure.
According to this fuel pump, the front wall surfaces of the blades which are inclined backward with respect to the rotational direction of the impeller conduct the fuel smoothly into the blade grooves, while the rear wall surfaces inclined in the same direction impart vigor to the fuel flowing out from the blade grooves. Further, the annular portion prevents stagnation of the fuel flow.
It is preferable that an angle of inclination of the front wall surfaces of the blades on one and the opposite side at the outer periphery portion is larger than that of the rear wall surfaces of the blades at an inner periphery portion. As a result, the admission and efflux of fuel into and out of the blade grooves become smoother.
In addition, preferably, an angle of inclination of the rear wall surfaces of the blades on one and the opposite side at the outer peripheral portion is larger than an angle of inclination of the rear wall surfaces from a side face at the inner peripheral portion, the angle of inclination of the front wall surfaces of the blades on one and the opposite side at the outer periphery portion is larger than that of the front wall surfaces at the inner peripheral portion, and/or the angle of inclination of the front wall surfaces of the blades on one and the opposite side is larger than that of the rear wall surfaces of the blades at the outer periphery portion.
Further, it is preferable that an angle of inclination of the front wall surfaces of the blades on one and the opposite side at an inner peripheral portion is larger than that of the rear wall surfaces at the inner peripheral portion.
Furthermore, preferably, an angle of inclination of the front wall surfaces of the blades on one and the opposite side at the outer periphery portion is larger than an angle of inclination of the rear wall surfaces from a side face at the outer periphery portion, and an angle of inclination of the front wall surfaces of the blades at an inner periphery portion is lager than that of the rear wall surfaces at the inner periphery portion.
According to the fuel pumps mentioned above, the removal of the die after molding the impeller becomes easier.
To achieve the second aspect of the invention, a first turbine type fuel pump is provided with an impeller of a disc shape. The impeller has blades, blade grooves, and an annular portion formed on an outer periphery side of the blade grooves. The blades and the blade grooves are formed alternately in a circumferential direction on one side and an opposite side of an outer periphery portion of the impeller. Front and rear wall surfaces of each of the blade grooves are inclined backward with respect to a rotational direction. The fuel pump further has a pump housing which houses the impeller therein rotatably. The pump housing has generally C-shaped side grooves on one and the opposite side which side grooves are in communication with the blade grooves on one and the opposite side respectively, a fuel suction port communicating with a start end portion of the side groove on one side, a fuel discharge port communicating with a terminal end portion of the side groove on the opposite side, start end-side communicating portions for communication between the start end portion of the side groove on one side and a start end portion of the side groove on the opposite side, and terminal end-side communicating portions for communication between a terminal end portion of the side groove on one side and the terminal end portion of the side groove on the opposite side.
With the first turbine type fuel pump, by rotation of the impeller, fuel is circulated independently between the side grooves and the blade grooves on one and the opposite side to increase the fuel pressure.
According to this fuel pump, the annular portion of the impeller and the communicating portions of the pump housing avoid stagnation and collision of fuel in a pump channel.
It is preferable to make the fuel flow at the start and end portions smooth that the communicating portions in the start end portions on one and the opposite side and the communicating portions in the terminal end portions on one and the opposite side are formed axially on outer periphery sides of the start and terminal end portions.
Further, to prevent the pulsation at the terminal end portion, preferably, the communicating portion in the terminal end portion of the side groove on one side has an inclined guide surface inclined in a direction to guide fuel present within the side groove to the terminal end portion of the side groove on the opposite side.
A second turbine type fuel pump is provided with an impeller of a disc shape. The impeller has one-side blades and blade grooves formed alternately in a circumferential direction on one side face of an outer periphery portion of the impeller, opposite-side blades and blade grooves formed alternately in the circumferential direction on an opposite side face of the outer periphery portion and in a circumferentially displaced state with respect to the blades and blade grooves on one side, and an annular portion formed on an outer periphery side of the blade grooves on one and the opposite side. The fuel pump further has a pump housing which houses the impeller therein rotatably. The pump housing has generally C-shaped side grooves formed on one and the opposite side and communicating respectively with the blade grooves formed on one and the opposite side, a fuel suction port communicating with a start end portion of the side groove on one side, and a fuel discharge port communicating with a terminal end portion of the side groove on the opposite side.
With the second turbine type fuel pump, by rotation of the impeller, fuel is circulated independently between the side grooves on one and the opposite side and the blade grooves on one and the opposite side to increase the fuel pressure.
According to this fuel pump, the pulsation of pressure at a terminal end portion of a pump channel is prevented by the annular portion of the impeller and further by a zigzag arrangement of one- and opposite-side blade grooves.
It is preferable to make the flow of fuel in the blade grooves smooth that the blade grooves on one and the opposite side are inclined backward with respect to a rotational direction.
To prevent the stagnation and collision of fuel, the blade grooves on one and the opposite side are, preferably, gradually decreased their spacings as a transversely central part is approached from side faces of the impeller.
To achieve the third aspect of the invention, a first impeller having a disc shape. An outer periphery portion of the impeller has a plurality of one-side blade grooves formed spacedly in a circumferential direction on one side face of the outer periphery portion, a plurality of opposite-side blade grooves formed spacedly in the circumferential direction on an opposite side face of the outer periphery portion and isolated from the one-side blade grooves, and a plurality of communicating holes extending through portions from the one to the opposite side face which portions are deviated radially inwards or outwards from the one- and opposite-side blade grooves.
According to this impeller, the one- and opposite-side blade grooves are not formed with communicating holes for allowing fuel to flow from the suction side to the discharge side. Therefore, it is possible to select such size and shape of one- and opposite-side blade grooves as can realize an optimum increase of fuel pressure independently of the selection of shape, etc. of communicating holes.
A second impeller has a disc shape. An outer periphery portion of the impeller has a plurality of one-side blades and blade grooves formed alternately in a circumferential direction on one side face of the outer periphery portion, a plurality of opposite-side blades and blade grooves formed alternately in the circumferential direction on an opposite side face of the outer periphery portion and isolated from the one-side blade grooves, an outer annular portion positioned on an outer periphery side of the one- and opposite-side blades, and a plurality of communicating holes formed in and extending through portions from the one to the opposite side face which portions are deviated radially inwards or outwards from the one- and opposite-side blade grooves.
According to this impeller, a partition wall portion for partitioning between one- and opposite-side blade grooves is not formed with communicating holes for the flow of fuel from the suction side to the discharge side. Therefore, characteristics of the outer annular portion and the one- and opposite-side blades can be selected so as to select such size and shape of the one- and opposite-side blade grooves as can realize an optimum increase of fuel pressure independently of the selection of shape, etc. of communicating holes.
It is preferable to increase the pressure of fuel efficiently with minimum pressure pulsation that the plural one-side blade grooves and the plural opposite-side blade grooves are displaced from each other in the circumferential direction.
Preferably, the plural communicating holes are formed radially inside the plural one-side blade grooves and the plural opposite-side blade grooves. Since the one- and opposite-side blade grooves are formed radially near the outer periphery and the radius of gyration becomes large, the pressure of fuel is increased effectively.
If the plural communicating holes are displaced in the circumferential direction from radial extension lines of the plural one- and opposite-side blade grooves, the one- and opposite-side blade grooves, which are displaced (in a zigzag fashion) in the circumferential direction, are communicated with each other through communicating holes.
The number of the communicating holes may be equal to or smaller than the number of the one- and opposite-side blade grooves. The same number of communicating holes as the number of blade grooves provide communication between one- and opposite-side blade grooves and a smaller number of communicating holes than the number of blade grooves provide communication between a portion of one-side blade grooves and a portion of opposite-side blade grooves.
A plurality of one-side shallow grooves and a plurality of opposite-side shallow grooves may be formed to communicate with the plural one- and opposite-side blade grooves and the plural communicating holes. In this case, the one- and opposite-side shallow grooves provide communication between one- and opposite-side blade grooves even in the case where one- and opposite-side blade grooves are in opposition to the communicating holes in the start and terminal end portions.
A plurality of axially projecting one-side projections and a plurality of axially projecting opposite-side projections may be formed between the plural one- and opposite-side blade grooves and the communicating holes so that a certain wall thickness is ensured between the one- and opposite-side blade grooves and the communicating holes and this thick-walled portion is difficult to undergo breakage, etc.
A plurality of one-side shallow grooves and a plurality of opposite-side shallow grooves may be formed in the plural one- and opposite-side projections to provide communication between the plural one- and opposite-side blade grooves and the communicating holes. Even where one- and opposite-side blade grooves are not in opposition to the communicating holes in the start and terminal end portions, one- and opposite-side shallow grooves formed in the one- and opposite-side projections provide communication between the one- and opposite-side blade grooves.
If the number of the one- and opposite-side shallow grooves is equal to or smaller than the number of the communicating holes, the same number of one- and opposite-side shallow grooves as the number of communicating holes provide communication between the communicating holes and the blade grooves and a smaller number of one- and opposite-side shallow grooves than the number of communicating holes provide communication between a portion of communicating holes and a portion of blade grooves.
The plural one- and opposite-side shallow grooves may be displaced in the circumferential direction from radial extension lines of the plural one- and opposite-side blade grooves and also from radial extension lines of the communicating holes so that one- and opposite-side shallow grooves provide communication between one- and opposite-side blade grooves formed in a zigzag fashion together with the communicating holes.
To achieve the third aspect of the invention, a turbine type fuel pump comprises an impeller having a disc portion and an outer periphery portion. The outer periphery portion includes a plurality of one-side blade grooves formed spacedly in a circumferential direction on one side of the outer periphery portion, a plurality of opposite-side blade grooves formed spacedly in the circumferential direction on an opposite side face of the outer periphery portion and isolated from the one-side blade grooves, and a plurality of communicating holes extending through portions from the one side face to the opposite side face which portions are deviated radially inwards or outwards from the one- and opposite-side blade grooves of the outer periphery portion. The fuel pump further comprises a pump housing which houses the impeller therein rotatably, the pump housing has a generally C-shaped one-side side groove and a generally C-shaped opposite-side side groove. The generally C-shaped one-side side groove extends from a one-side start end portion up to a one-side terminal end portion. The one-side start end portion is provided with a first communicating portion opposed to one-side openings of the plural communicating holes and is in communication with a fuel suction port. The one-side terminal end portion is provided with a second communicating portion opposed to the one-side openings. The generally C-shaped opposite-side side grooves extends from an opposite-side start end portion up to an opposite-side terminal end portion. The opposite-side start end portion is provided with a third communicating portion opposed to opposite-side openings of the plural communicating hole. The opposite-side terminal end portion is provided with a fourth communicating portion opposed to the opposite-side openings and is in communication with a fuel discharge port. The fuel pump further comprises a motor for rotating the impeller within the pump housing.
With the fuel pump mentioned above, a portion of fuel which has entered the first communicating portion flows to the third communicating portion through the communicating holes, fuel flows from the one- and opposite-side start end portions to the one- and opposite-side terminal end portions, and fuel in the second communicating portion which fuel has been increased its pressure flows to the fourth communicating portion through the communicating holes.
In this fuel pump, a portion of fuel which has entered the first communicating portion flows to the third communicating portion through communicating holes formed in the impeller. Consequently, the fuel flows spirally from one- and opposite-side start end portions to one- and opposite-side terminal end portions while circulating between one-side blade grooves and one-side side groove and between opposite-side blade grooves and opposite-side side groove. The fuel in the second communicating portion, whose pressure has been increased, flows to the fourth communicating portion through communicating holes formed in the impeller. As a result, there is attained a high pump pressure and the application of a radial force to the impeller, which is caused by the pressure of fuel flowing in the communicating holes, is prevented.
To make the formation of one- and opposite-side side grooves easier, it is preferable that the pump housing comprises a first housing located on the suction side and having a lid shape and a second housing located on the discharge side and having a container shape.
Preferably, the first and second communicating portions in the first housing are formed radially inside of the one-side start end portion and terminal end portion and have a radial length corresponding to the plural communicating holes.
Further, the third and fourth communicating portions in the second housing are formed radially inside of the opposite-side start end portion and terminal end portion and have a radial length corresponding to the plural communicating holes. In this case, the communicating portions in one- and opposite-side start and terminal end portions are opposed to one- and opposite-side openings of communicating holes formed radially inside of one- and opposite-side blade grooves in the impeller, whereby the flow of fuel from the opposite-side side groove to the one-side side groove is promoted.
To achieve the fourth aspect of the invention, a first impeller has a disc shape, and an outer periphery portion thereof includes a plurality of one-side blades and blade grooves formed alternately in a circumferential direction on one side face of the outer periphery portion, a plurality of opposite-side blades and brade grooves formed alternately in the circumferential direction on an opposite side face of the outer periphery portion, and a plurality of communicating holes extending through portions from the one to the opposite side face which portions are deviated radially inwards or outwards from the one- and opposite-side blade grooves of the outer periphery portion.
With the first impeller mentioned above, axial tip end portions of the one- and opposite-side blade grooves extend beyond an axially intermediate portion of the impeller.
Further, a second impeller has a disc shape, and an outer periphery portion thereof includes a plurality of one-side blades and blade grooves formed alternately in a circumferential direction on one side face of the outer periphery portion, a plurality of opposite-side blades and blade grooves formed alternately in the circumferential direction on an opposite side face of the outer periphery portion, and an annular portion positioned on an outer periphery side of the one- and opposite-side blades. The one- and opposite-side blade grooves are axially overlapped each other in a section including an axis of the impeller.
According to these impellers, such characteristics of blade grooves as can realize higher pump efficiency can be determined independently of characteristics of the communicating portions. Besides, it is possible to ensure such a blade groove shape as increases the momentum of fuel in the blade grooves.
If front and rear wall surfaces of the one- and opposite-side blade grooves are inclined backward with respect to a rotational direction, the admission of fuel into the blade grooves becomes smooth and vigor is imparted to the fuel flow at the time of efflux.
Further, if the one- and opposite-side blade grooves are displaced from each other in the circumferential direction, the fuel pressure can be increased effectively with minimum pulsation of pressure.
Furthermore, if a plurality of communicating holes extending through the outer periphery portion from the one side face to the opposite side face are formed, characteristics of the blade grooves can be determined independently of characteristics of the communicating holes.
The plural communicating holes may be deviated in the circumferential direction from radial extension lines of the one- and opposite-side blade grooves so that the one- and opposite-side blade grooves arranged in a zigzag fashion can be communicated with each other in a satisfactory manner.
Moreover, if the annular portion is formed with a plurality of one-side shallow grooves and a plurality of opposite-side shallow grooves to provide communication between the plural one- and opposite-side blade grooves and plural communicating holes, the one- and opposite-side blade grooves are communicated with each other through shallow grooves even if they are not opposed to the communicating holes.
Another turbine type fuel pump comprises an impeller of a disc shape, an outer periphery portion of the impeller including a plurality of one-side blades and blade grooves formed alternately in a circumferential direction on one side face of the outer periphery portion, a plurality of opposite-side blade grooves formed alternately in the circumferential direction on an opposite side face of the outer periphery portion, and a plurality of communicating holes extending through portions from the one to the opposite side face which portions are deviated radially inwards or outwards from the one- and opposite-side blade grooves of the outer peripheral portion, axial tip end portions of the one- and opposite-side blade grooves extending beyond an axially intermediate portion of the impeller. The fuel pump further comprises a pump housing which houses the impeller therein rotatably, the pump housing having generally C-shaped one- and opposite-side side grooves corresponding to the one- and opposite-side blade grooves respectively, a fuel suction port communicating with a start end portion of the one-side side groove, and a fuel discharge port communicating with a terminal end portion of the opposite-side side groove.
With the fuel pump mentioned above, by rotation of the impeller, fuel is circulated between the side grooves and the one- and opposite-side blade grooves to increase the fuel pressure. According to this fuel pump, such characteristics of the blade grooves as can realize higher pump efficiency can be determined independently from characteristics of the communicating portions. Besides, it is possible to ensure such a blade groove shape as increases the momentum of fuel in the blade grooves.